At suitable geographical sites, generation of electrical power can be accomplished-more or less economically--by converting energy available from stream-collected rainfall, tidal, or solar sources, substantially free of harmful emissions. More usually, electrical power is generated through combustion of fossil fuels, whether in gaseous, liquid, or solid form (e.g., natural gas, gasoline, coal), but such fuel combustion is accompanied by harmful emissions, also in gaseous, liquid, or solid form (e.g., nitrogen oxides, sulfurous acid, carbonaceous particulates). Carbon monoxide, often present as a harmful emission in the effluent from combustion of a fossil fuel, is so readily oxidizable that--when a fuel--it converts readily and substantially completely to harmless carbon dioxide upon combustion.
Incompletely combusted carbonaceous fragments or fossil fuel combustion by-products--whether gaseous, liquid, or solid--can be directly injurious to health of humans and other living creatures, as when breathed or ingested in or with food, and can be indirectly deleterious, as by altering characteristics of the biosphere upon which all living creatures depend. Polluting emissions from fossil-fueled factories and vehicles supplement those from electrical power plants, so there is an extreme need for both stationary and mobile power generation by alternative fuels whose combustion does not emit harmful gases, liquids, or solids. Combustion products considered harmless (as compared with aforementioned or other harmful examples) are notably carbon dioxide (gaseous) and water (gaseous or liquid).
Hydrogen, which has long been considered likely to be an ideal fuel because it converts completely to water in ordinary air combustion, is not satisfactory as fuel for internal combustion engines because it heats intake valves so hot that pre-ignition flashback occurs ahead of the combustion chamber, forming harmful nitrogen oxides then exhausted as emissions. See, to this effect, HYDROGEN STORAGE AND UTILIZATION IN TRANSPORTATION VEHICLES--SUMMARY, which was published in 1988 by the Alternative Fuels Utilization Program of the Office of Transportation Systems in the U.S. Department of Energy, including citation of other pertinent references.